1. Field of the Invention
This invention relates to heat pump systems in which a circulating fluid allows excess heat due to varying needs for heating and cooling in particular zones to be shared between the zones for greater efficiency. In particular, the invention relates to such a system having a storage reservoir for waste heat, the reservoir being maintained at temperatures substantially higher than the temperature of the circulating fluid.
2. Description of the Prior Art
Heating and/or air conditioning systems in which excess energy is shared among individually-controlled heat pumps for a number of heating zones are known in the art. Examples of such systems include those of U.S. Pat. Nos. 3,523,575-Olivieri, 3,407-620-Lodge, 3,404,728-Laube, and 3,165,148-Soule. The temperature control systems of these patents allow heat extracted from the air in one zone of the building, for example, on the side exposed to the sun, to be routed via a circulating heat transfer fluid to other zones which require additional heat, for example, on the shady side of a building. Heating and cooling efficiency is substantially increased because the individual heat pumps are not adapted to directly dissipate waste heat. Instead, the individual units transfer waste heat into the heat circulating fluid. Only when the overall loop of circulating heat transfer fluid reaches a predetermined temperature is the heat dissipated, for example using a rooftop cooling tower.
Circulating-fluid building heating systems are useful for equalizing time imbalances in heating needs, as well as the foregoing spacial imbalances between needs of individually-controlled zones. Such imbalances may be a result of weather conditions, or the result of the imbalances in heating requirements produced by variations in use of lighting and other incidental heat generating facilities. Waste heat produced by people and by use of equipment can be accumulated in the circulating heat transfer system, to be extracted when needed, for example at night when the building is largely unoccupied and the various heat generating devices not operating.
The aforesaid patent to Olivieri teaches increasing the heat storage capability of such a water-source heat pump system by including a tank for storing an excess quantity of the heat transfer fluid. The excess fluid in the system constitutes a heat sink capable of smoothing at least a portion of the imbalances in heating requirements, providing a more efficient system. The capability of smoothing imbalances will be related to the extent of imbalance, and the mass of the thermal sink.
As heat is extracted from zones in the building by the circulating heat transfer fluid, which constitutes the thermal sink, the temperature of the fluid continuously rises. Inasmuch as the efficiency of individual zone heat pumps is directly related to the difference in temperature between the evaporator and condenser, overall efficiency will suffer if the temperature of the heat sink, that is, the mass of heat transfer fluid in the heat transfer loop, is allowed to become too high. The system designer of the water-source heat pump system including a quantity of excess fluid as a heat storage reservoir, is inclined to employ as large a reservoir as can be managed. The need for a large mass concerns both a need for large heat storage capacity to smooth large imbalances, and a need to keep the temperature of the heat transfer fluid as low as possible during times of maximum heat storage.
It is theoretically possible to employ a heat energy reservoir of sufficient size to completely smooth over all time and space imbalances in heating requirements. Such a system would go so far as to accumulate waste heat during the summer months for dissipation during the winter months. In view of the storage requirements and the decrease in efficiency at high heat transfer fluid temperatures, a reservoir of sufficient size would be impractical. Therefore, the efficiency of prior art systems, or their ability to accumulate a large quantity of excess heat for later extraction, has been limited.
According to the present invention, the basic system of a water source heat pump with a heat storage reservoir is made substantially more efficient by at least partly separating the thermal reservoir from the circulating heat transfer fluid, and allowing the reservoir to reach a much higher temperature. The circulating heat transfer fluid and the reservoir are joined by a connecting heat pump disposed between the circulating fluid and the reservoir fluid. The connecting heat pump extracts heat from the circulating fluid for deposit in the reservoir, stepping up the temperature of the reservoir over the temperature of the circulating fluid. Accordingly, at such higher temperatures, a substantially greater quantity of heat can be efficiently stored in a thermal sink of a given size. Means are provided for extracting the heat from the sink for useful purposes, including controllably bleeding the high-temperature reservoir fluid back into the circulating fluid system, and/or connecting separate heating loads such as potable water heaters by means of heat exchange devices.
The system of the invention is quite efficient in that minimum use is made of the system's rooftop cooling tower for cooling and boiler for heating, otherwise required to provide sufficient energy, or to extract sufficient energy, for operation of the individual zone heat pumps. The use of the higher-temperature heat storage reservoir connected via a heat pump provides dual benefits of higher storage capacity as well as increased efficiency of the individual heat pumps resulting from lower temperature heat transfer fluid.